ECE 583 Lecture 27 Imaging Visible and Infrared Radiometers Array Detector Imagers Stereo Cloud Hieght & Winds Application
Why remote sensing - Much of the atmosphere is inaccessible, at least for routine measurements. From space, only way to provide large enough sample to large-scale view of the Earth system AVHRR SST anomalies Nov 96,97
Measurement Requirements for Imaging Radiometers Spatial resolution (pixel size) Number and wavelength of channels Spectral width of wavelength channels Spatial alignment (registration) between wavelength channels Minimum signal measurement accuracy (%) Measurement accuracy of radiance (calibration) Basic Type of Image Scanning Radiometer
Pushbroom Imaging Whiskbroom Imaging Grating Spectrometer Pushbroom Imaging
Example of MISR Level 2TC data product Hurricane Debby Level 2 Top-of- Atmosphere/Cloud Product This contains measurements of cloud heights and winds, cloud texture, top-ofatmosphere albedos and bidirectional reflectance factors, and other related parameters.
Low Earth Orbit Stereo Imagers VISIBLE MISR visible push broom imager, large angle separation tri-angle wind retrieval THERMAL INFRARED ATSR 45 o conical scan, 120 sec image separation, ESA ISIR 8-12 o angle separation, ¼ km resolution, 90 km cross track 260 km orbit height, STS-85 ICIR 10 o angle separation, 0.65 km resolution, 1400 km cross track 820 km orbit height, Proposed
Planck s blackbody function The nature of B λ (T) was one of the great findings of the latter part of the 19th century and led to entirely new ways of thinking about energy and matter. Early experimental evidence pointed to two particular characteristics of B λ (T) which simplify calculations. Insert fig 3.1 B B λ λ C C 1 2 2πhc = 5 hc/ λ πλ (e = πλ 5 (e = 2πhc C kt 1 C / λt 2 2 2 1) 1) = 3. 7141832 10 = 3. 7141832 10 = 3. 7141832 10 = hc/k = 1438786. μm K 8 4 W μm 4 4 W μm 4 W nm m 2 cm 4 m 2 2
Brightness temperature An important temperature of the physical system, and one different from the thermodynamic temperature in general is the temperature that can be attached photons carrying energy at a fixed wavelength. If the energy of such is I λ, then this temperature is T λ = B -1 (I λ ) = C 2 /{λln[i λ λ 5 π/c 1 +1]} which is referred to as the brightness temperature The brightness temperature of microwave radiation is proportional in a simple way to microwave radiance: Rayleigh Jeans Law λt B(T) kt The spectral brightness temperature of planets and moons
IR Stereo Imager Development Global Infrared Stereo Observations by LEO UMAD Imaging Radiometer ISIR Shuttle Hitchhiker Experiment COVIR Instrument Incubator Multi Layer Stereo Retrievals
Application: Diurnal Variation in Cloud Height Distribution Diurnal variation is a huge factor for cloud distributions. The best passive retrievals use visible plus IR channels, not possible at night. IR only CO 2 slicing retrievals are limited in resolution. Active sensors, lidar/radar, now measure nadir only. Scanning radar/lidar is high cost and limited to a few 100 km s.
Goal 1, Low cost IR cloud imager Goal 2, Stereo Cloud IR in LEO Goal 3, Improved cloud track winds Velden et al., 2005, Bul. AMS The impact of satellite-derived polar winds in global forecast models David A. Santek, CIMSS/Univ. of Wisconsin, Madison, WI The use of Atmospheric Motion Vectors (AMVs) in Numerical Weather Prediction (NWP) models continues to be an important source of information in data sparse regions. These AMVs are derived from a time-sequence of images from geostationary and polar orbiting satellites. NWP centers have documented positive impact on model forecasts not only in regions where the AMVs are measured, but elsewhere as well. One example is the effect of the Moderate Resolution Imaging Spectroradiometer (MODIS) polar winds on forecasts in the middle and subtropical latitudes. Feature-tracked winds derived from a time-sequence of MODIS satellite imagery over the polar regions are routinely input into many operational global numerical models. These NWP centers report that the winds have a positive impact on forecasts not only in the polar regions, but also into mid- and lower-latitudes, especially in 3 to 5 day forecasts. However, the impact differs for different models. Side-by-side experiments were run, with and without MODIS polar winds, using the National Centers for Environmental Prediction's (NCEP) Global Forecast System (GFS) and the Navy's Operational Global Atmospheric Prediction System (NOGAPS) models. Output from these experiments was analyzed by using a combination of model analyses and forecasts, with sophisticated visualization techniques, to determine the impact to global model fields. The differences in these model fields between the GFS and NOGAPS due to the inclusion of the MODIS winds are explained by data thinning, weighting of the wind observations, and characteristics of their respective assimilation systems.
Space Shuttle Experiment for Uncooled IR Array Infrared Spectral Imaging Radiometer (ISIR) Objectives: Develop Compact, Low Cost and Rugged Imaging Infrared Cloud Radiometers Test the Application of Uncooled Microbolometer Focal Plane Arrays for Space Borne Imaging Applications Observations For Cloud Science: Obtain Combined Passive/Active Remote Sensing From Joint Shuttle Flight with the SLA Lidar Specifications: Microbolometer array detector eliminates cooling requirements Push broom imaging eliminates mechanical scanning Time delay integration improves NEDT by the square root of the along track detector elements 8, 11, 12 & 7-147 μm m channels, 0.1-0.01 0.01 o K NEDT, 250 m resolution, 82Km swath Microbolometer Array
Uncooled Microbolometer Array Detector (UMAD) Technology was originally declassified in about 1990. The ISIR detector was the second pre-production array produced by Loral Space Systems.
Uncooled Microbolometer FPA
Altitude ~ 250 km
ISIR - Time Delay and Integration (TDI)
Image Signal as a Function of Lens/Telescope F# P pix (λ) = I(λ) A Ω T sys P = Pixel Signal in Watts F# = L/D A = π D 2 /4 D= Lens Diameter Ω= π (d/l) 2 /4 d = Pixel Diameter L = Focal Length Low F# lens gives brightest imageneeded for higher noise detectors. ISIR Lens: F =.73 Theoretical Minimum F =.6 P pix (λ) = I(λ) (d π / 4F# ) 2 IR imaging radiometer showing refractive telescope and electronics imaging module
ISIR prior to shuttle Hitchhiker bridge installation 8 mm tape drive
87 km swath
Shuttle Roll Maneuvers with ISIR in Video Camera Mode
ISIR 10.8 um Channel (Coast of New Jersey) 80 km (50 mi) 145 km (90 mi)
ISIR Multispectral Analysis 262 K 281 K Temperature (K) Cirrus Particle Size from IR Split Window Brightness Difference
ISIR on STS-85 ISIR SENSOR ASSEMBLY ZnSe WINDOW UPPER END PLATE ADAPTER PLATE RECORDING DEVICE Proved uncooled IR array detectors for space First global multispectral IR data set at 1/4 Km resolution Global cloud science with laser altimeter cloud heights LOWER END PLATE
Mars Surface Imager Based On Microbolometer array detector
Stereo Height Retrieval Spectral band at moment of image capture Band 1 = 8.6 um Band 3 = 12.0 um 1 3 10.4 degrees FOV ISIR Trajectory Height ~ 260 km ~ 79 km 325 columns ground track at nadir 50 % overlap ~100 rows at sea level ~ 48 km 204 rows Figure 2. Stereo overlap of ISIR image frames acquired at 8.6 and 12 mm roughly 3.5 seconds apart. This gives 50% overlap and complete ground coverage between the two spectral bands calculate the height of any feature in the overlapped region from its measured parallax in pixels as: h = H B δ *θ
Lancaster et al., 2003 Stereo Height Retrieval
The depth resolution attainable with this method can be expressed in terms of the range-to-baseline ratio and the IFOV. For ratios greater than 30, the depth resolution degenerates to one baseline. The equation below shows the relationship between baseline B; range Z; IFOV, and depth resolution ΔZ/B, for a pixel located at the center of the overlapped region. Simple geometry and trigonometry results in the expression: ΔZ = B 1 2 1 tan(arctan( 2 B Z 1 θ B ) ) tan(arctan( 2 2Z θ ) + ) 2 This equation can be used to give height uncertainty in km as a function cloud height h, by replacing the range Z with (H - h). The figure shows the results for an altitude of 266 km, a baseline of 25.9 km and 0.903 milliradian IFOV. For a single-pixel cloud at 10 km altitude, the height uncertainty would be +/_ 2.3 km (without using a sub-pixel algorithm to search for the parallax giving the best correlation between views). 2.5 2.45 2.4 height uncertainty in km 2.35 2.3 2.25 2.2 ISIR IFO V 0.903 m rad, altitude 266 km, baseline 25.9 km 2.15 2.1 0 2 4 6 8 10 12 14 16 18 20 cloud altitude in km Depth resolution expressed as ± height uncertainty for clouds ranging between sea level and 20 km. Graph is for ISIR stereo imaging.
234 245 256 267 278 3500 Brightness Temperature (K) 5500 7500 9500 Altitude (m) 11500
ISIR Cloud Heights from Stereo Analysis Compared to Shuttle Laser Altimeter Cloud Heights Laser Stereo
Issues for Stereo Accuracy Measurement physics: Photon penetration / Distributed source function Multi cloud layers Cloud top contrast Cloud motion Instrument issues IFOV and stereo view separation NEDT Height uncertainties driven by measurement physics
1000 8.6 um Tbr Histogram number of pixels 800 600 400 200 0 230 240 250 260 270 280 290 Tbr in K 12 um Tbr Histogram 1000 number of pixels 800 600 400 200 Figure 4. Composite imagery at 8.6 and 12 um, comprised of two frames in each band. Only the regions of overlap are shown. The motion of the ISIR sensor is from the bottom towards the top of the panels. 0 230 240 250 260 270 280 290 Tbr in K Figure 5. Brightness temperature histograms of composite thermal images in Figure 4.
8.6 micron ROI masks 12 micron ROI masks Figure 6. Binary ROI (region-of-interest) masks for the stereo pair in Figure 4 are shown, created by assigning a value of 1 to all pixels at or below the indicated brightness temperature, and 0 to all pixels above that temperature. The highest clouds are in the masks at the top of the frame, and are arranged in order of increasing temperature, and hence decreasing altitude.
Figure 8. Discrete height maps generated from ROI masks and stereo retrieval. The altitudes are tabulated in the table above.
Figure 12. 8 um stereo height composite and line plot of stereo heights along nadir column for composite image obtained between 8:17:18:55:31 to 8:17:18:58:04 GMT, or from 90 W, 50 N, to about 60 W, 30 N.
Stereo Retrieval Research Multiple Cloud Level Profile Retrieval Objective: Identify common cloud layers for stereo height retrieval Approach: Exploit correlation between infrared T B and cloud height - Define cloud mask based up T B - Identify parallax shift for cloud mask thru pattern matching - Assign retrieved height to all pixels enclosed by mask 2 Result: Stereo height retrieval for multiple cloud layers 3 3 cloud layers 1 2 3 1 Manizade et al., 2005
Free Flyer Prototype Development Compact Visible and Infrared Radiometer Optic Bench Visible Camera Assembly 45 cm ½ km resolution from 600km four IR channels between 3.5 and 12.5 um IR detector: Uncooled, microbolometer Focal Plane Array Flip mirror Assembly Internal Blackbody IR Detector Electronics IR Camera Assembly Separate visible and infrared cameras Array detector pushbroom imaging Time Delay and Integration to improve S/N 0.1 o K accuracy at 300 K up to four visible channels between 440 and 860 nm Visible detector: Uncooled, CCD linear array Mass: 20 kg; Power: 35 W
COVIR Design Upgrades Move from a filter wheel design to using strip filters 10 μm 10.8 μm 12 μm 3.7 μm Strip Filters Detector Array TEC Cooler Fig. 2 Conceptual drawing of detector assembly Eliminates dead time between filters - Allows for inclusion of 4 th passband with TDI 15 Eliminates possible mechanical failure of the filter wheel. - Provides greater reliability
Detector Specifications Infrared 60 pixels 60 pixels 60 pixels 60 pixels Type Uncooled microbolometer FPA Format 327 x 240 Operation Time Delay and Integration Channels 4 Visible Type CCD linear array Format 4 rows of 1x1520 Operation Continuous readout Channels 4 8.0-9.0 micron channel 10.3-11.3 micron channel 11.5-12.5 micron channel 3.55-3.95 micron channel 320 pixels 240 pixels Figure 3 Microbolometer array with strip filters
Optics: Calculations and Trade Studies Analysis: Vignetting calculations for filter strips indicate possible TDI frame rates as a function of F/#: Design Support: Design support for the detector sub-assembly: optical path lengths, element spacings, and materials: sapphire Step A/R Coated Germanium Window 0.5mm { Detector { vignetted region = 3.4 pixels same { vignetted region { vignetted region = 17 pixels Not to Scale } 0.5mm } 0.125 mm 3.5 3.9 μ Strip Filters Filter Substrate 10 μm 10.8 μm 12 μm DetectorArray TEC Cooler 3.7 μm 15 mils 3-5 mils Ghost Images: calculations to determine guidelines for element spacing: Detector 11.5 12.5μ 10.3 11.3μ θ 8.5 10.5μ L { s { s { s { s s s s
IR Optical Prescription Data: F/0.8; Focal length = 55.52 mm; Aperture = 69 mm A triplet lens design solution: Spotsize Goal = 46 μ; Design Result = 35 μ Encircled energy = 80% IR Lens Mount (Janos):
Compact Visible and Infrared Radiometer IR Imaging radiometer is built around an uncooled microbolometer array detector (UMAD) Technology benefits: No cooling = low power consumption No cooling = no thermal radiators Focal plane array = Simultaneous 2D imaging Focal plane array = compact, lightweight Focal plane array = stereo imaging Focal plane array showing bandpass filters prior to installing germanium package window Proposed IR Camera Type of Imaging Detector Format Pixel Size Frame Update Rate Telescope Number of channels NEDT Design Parameter Pushbroom Uncooled microbolometer FPA 320x240 pixels 46.25 um 60 frames/second Refractive, F/0.9 4 (11um, 12umx2, 3.7 um) 0.1 o K IR imaging radiometer showing refractive telescope and electronics imaging module
Compact Infrared and Visible Imaging Radiometer -COVIR Small Multispectral Infrared and Visible Imaging Radiometer Cloud and Surface Observations With Combined Spectra and Spatial Imaging Follow on to ISIR-01 experiment on STS-85 Instrument Incubator Project - Engineering Model Development Objective: Moderate resolution (1/2km) 5 channel visible and near infrared imaging Combined spatial and spectral IR imaging Small size and low cost 6
Flight Mission Instrument Development Compact Visible and IR Imaging Radiometer Vertical Imaging Cloud Infrared Imager CoVIR IIP Instrument Flight Breadboard 200 km Swath
Mission Proposal Design Study SIRICE IR Imaging Radiometer PUSHBROOM SCANNING RADIOMETER IR camera stares nadir or at an angle (fore or aft) Image is sampled sequentially in each of the 3 spectral channels Time Delay and Integration is used to achieve NEDT < 100 mk Image spatial resolution ~ 1.5 km/pixel Two (possibly three) cameras needed to cover 90 o FOV TECHNICAL CHALLENGES: Calibration of the multiple cameras Use of TDI requires spacecraft attitude be controlled to align image motion with 1 dimension of detector array PRACTICAL BENEFITS: Natural mode of operation for 2D array GSFC has developed two of these systems already Most of the technical challenges have been worked out Cross-track direction FOV of sub-mm conical Scanner 1400 km FOV Camera 3 FOV Camera 2 FOV Camera 1 3 IR spectral channels Ground-track of sub-mm conical scanner
IRCIR Development Three or four cameras based on COVIR design Each camera covers a 30 degree swath with a max 22.5 fore-aft angle for stereo Basic 1 km resolution with onboard compression and possible stereo processing GSFC PI and management Cost competition build options: - University and GSFC partnership - GSFC in house - Contracted to industry
IRCIR Characteristics Signal to Noise Ratio Current UMAD technology: 100 COVIR Spectral Channels NEDT ~ (200/Δλ)(F/#) 2 mk μm For λ~11 um, 300K scene, F/1 SIRICE Requirements: 1 um passband filters Three channels 11 um, 12um, 7 um NEDT < 100 mk Transmission (Percent) 90 80 70 60 50 40 30 20 10 0 3000 3184 3368 3552 3736 3920 4104 4288 4472 4656 4840 9046 9414 9782 10150 Wavelength (nm) 10518 10886 11254 11622 11990 12358 12726 13094 13462 SIRICE Results: Wavelength (um) 11 12 7 NEDT (mk) (No Averaging) 190 mk 350 mk 243 mk NEDT (mk) (w/ Averaging) <100 mk <100 mk <100 mk Need 3x improvement in SNR Include 10 pixels in TDI average ( 10 ~ 3) Resample single pixel 2x in 0.3 s scan time at 60 fps with <1/10 pixel registration error (SNR increases by 2 ~1.4)
IRCIR Global LOE Cloud Imager Mirrors rotate ~45 deg off-nadir to view cloud scene TDI Mirrors rotate ~270 off-nadir to view blackbody calibration source Mirrors rotate ~80 off-nadir to view space for calibration measurement Camera 1 Camera 2 Camera 1 Camera 2 45 deg Camera 3 Camera 4 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Resolution (km) Camera 3 Camera 4
Infrared Cloud Imaging Radiometer VIRCIR Concept 1400 km Swath Cloud Retrieval 14.4 cm 4 rotating mirrors Servo-motor, capstan drive combo 24.3 cm 14.1 cm 17.3 cm Electronics box Front View 18.3 cm Camera Heads 4 Calibration blackbodies 18.4 cm Camera Heads
IRCIR Instrument Concept for Stereo Cloud Track Winds 4 Imaging Arrays With associated Lens assemblies Optics Bench Rotatable Scene Mirror Science IR Cloud Information Stereo Cloud Height Winds (flying in orbit with NPP) Protective Drum Baffle (rotates with Scene Mirror) Cross-track Fields of View IRCIR Provides Full Cross-track Coverage using Four 640 x 480 pixel Uncooled Silicon Micro-bolometer Arrays
IRCIR Located on Dedicated Deck Behind SM4 This view of the instrument is rotated about the S/C axis by 90
Advanced Technology GOES Imager 101.6cm 75cm Meets all present GOES Imager Requirements Imaging Radiometric Performance Envelope Mass, Power Development Schedule 27 months to flight unit delivery Integration of modern (available) hi-reliability components 81.28cm
Rapid Response IR/Visible GOES Meteorological Imager Instrument Characteristics 5 band Step-Staring Imager IFOV: 4 km (IR) /1 km (vis) FOV: 1000 km x 960 km (Present 320x240 LW FPA) Field of Regard: +/- 20 deg. 4-band IR radiometer (~ 7, 11,12, 13.5 μm with uncooled IR FPAs, 3.9 μm with high temperature(190k) HCT FPA) 1-band visible (CCD) Technology and Programmatic Readiness Favorable Accomodation Parameters Technology for all instrument components is sufficiently mature (NASA TRL 7 or higher).. Preliminary investigation of instrument/spacecraft interface shows no notable concerns. Schedule, while aggressive, is consistent with other programs of similar complexity. <90 kg/ 0.4 m 3 / 100 W, and no cryo radiators! 66
NESR for 10.8 μm Channel (Standard LW Window) Detector NEP: 3.5 pw/(hz) 1/2 System Transmission: 50% Detector Area: 46x46 μm Solid Angle: (f/1.4) Noise Bandwidth: 7.5 Hz (4) Modulation Frequency: 10 Hz Incoherent Sample Summing Improvement Factor: (20) 1/2 Spectral Pass Band: 88 cm -1 NEP (W/rt Hz) 28 Micron Square Uncooled Bolometer NEP 1.00E-10 1.00E-11 1.00E-12 1.00E-13 1.00E-14 0.1 1 10 100 1000 10000 100000 Frequency(Hz) NEP_Thermal NEP_johnson NEP_1/f pix Predicted NESR: <0.07 mw/str/m 2 /cm -1 Required NESR: 0.272 mw/str/m 2 /cm -1 (200 mk NEDT @ 300K)
JEM Attached Payload Modules